The present invention relates generally to printing methods and apparatus, and can relate in certain aspects to ink drying methods and apparatus as applied in the context of inkjet printing operations.
Inkjet printing produces print imaging by propelling ink droplets onto media. A variety of inkjet printing mechanisms have evolved, but generally share in a common characteristic of rendering an image by depositing liquid ink, e.g., ink formulations including evaporatable components, on a media substrate. As such, inkjet printing methods and operations sometimes include drying of media, e.g., drying liquid ink to remove evaporatable components following application thereof to media. Thus, the “wet” nature of ink as applied to produce print imaging by inkjet printers has lead to the development of ink drying systems.
Inkjet drying techniques include passing media with wet print imaging against or near heated rollers and platens. Wet print imaging will smudge, however, if the drying apparatus contacts the print imaging. The application of heat energy and consequent drying of wet media when in a curved condition, i.e., as wrapped against a roller, often results in undesirable cockling and/or buckling or curvature of output. As a result, such media often suffers in quality and in some cases requires additional processing to flatten the media.
Generally, application of heat energy to wet ink volatilizes the ink and thereby dries print imaging produced thereby. Unfortunately, volatizing ink produces ink vapor which may contaminate a printing operation and may inhibit further drying. Volatilized ink compounds are sometimes carried away from a printing operation to reduce buildup of such compounds as volatilized or as settling back on or about various surfaces. Thus, some ink drying methods and apparatus contain or otherwise carry away volatized ink compounds to avoid contamination of the printing operation.
Volatilized ink compounds can inhibit further drying when accumulated at the media surface. Volatized ink compounds sometimes accumulate to form a boundary layer or cloud at the media surface. This body of volatilized ink sometimes inhibits further volatilization of ink and thereby sometimes inhibits further drying of print imaging.
Earlier ink drying systems avoid direct contact with print imaging while being dried. Paper transport mechanisms and other related paper handling paper mechanisms, e.g., such as to hold media well against a reference or support surface or platen, maintain a given distance between the printhead orifice plate and the media print surface. Direct contact with print imaging prior to it being suitably dry can result in undesirable smudging and degradation thereof, as was the case in earlier media handling systems, such as those using star-wheels in the media output path.
Ink formulations have been developed for improving drying time for inkjet printing applications. In addition to ink formulations, certain methods of printing have evolved to improve ink drying time in inkjet printing applications. As noted above, some inkjet printers include elaborate heating devices through or upon which media pass following application of print imaging. Ink formulations, drying mechanisms, and printing techniques directed toward improved ink drying time, however, sometimes present undesirable side effects. There can exist, therefore, a compromise between drying time and other print imaging quality requirements, as well as printing throughput, a performance rating usually measured in pages per minute.
Thus, many inkjet printing operations improve by reducing print image drying time. Preferably, this is accomplished without significantly compromising other print image quality requirements. Inkjet printing operations sometimes accomplish improvement by incorporating elaborate ink drying devices and methods. In some cases, fast-dry ink formulations, e.g., including special or more volatile evaporatable components provided for the purposes of ink drying, as opposed to print imaging purposes, have been used to improve ink drying time. Even inkjet printing operations including use of ink formulations having relatively fast drying time can benefit, however, by additional steps applied to print imaging to more quickly vaporize evaporative components thereof.
Printing operations making use of such fast-dry ink formulations do benefit, therefore, when drying procedures are applied to print imaging formed thereby. Expensive and elaborate ink drying systems, however, are not as easily justified for use in conjunction with expensive fast-dry inks. Given an investment in fast-dry inks, further investment in elaborate ink drying systems may be partially redundant and, to some extent, can in some cases represent an inefficient use of resources. As a result, ink drying systems typically are not used in conjunction with printing operations making use of expensive fast-dry inks.